# CVE-2021-38505: Mozilla Firefox ESR and 3 others: Microsoft introduced a new feature in Windows 10 known as Cloud Clipboard which, if enabled, will record…

CVE-2021-38505 is fixed in 2 products on 1 platform, first by Mozilla Thunderbird (en-US) 91.3.0, released November 1, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-38505
- Priority: Routine
- CVSS: 6.5
- EPSS: 0.0108
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Dec 8, 2021
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-38505

## Description

Microsoft introduced a new feature in Windows 10 known as Cloud Clipboard which, if enabled, will record data copied to the clipboard to the cloud, and make it available on other computers in certain scenarios. Applications that wish to prevent copied data from being recorded in Cloud History must use specific clipboard formats; and Firefox before versions 94 and ESR 91.3 did not implement them. This could have caused sensitive data to be recorded to a user's Microsoft account. *This bug only affects Firefox for Windows 10+ with Cloud Clipboard enabled. Other operating systems are unaffected.*. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Windows apps | Mozilla Firefox ESR (en-US) | 102.0 | [Mozilla Firefox ESR (en-US) 102.0](https://patchblox.com/security/data/fix/windows-app/mozilla.firefox.esr-102.0.md) | Jun 23, 2022 |
| Windows apps | Mozilla Thunderbird (en-US) | 91.3.0 | [Mozilla Thunderbird (en-US) 91.3.0](https://patchblox.com/security/data/fix/windows-app/mozilla.thunderbird-91.3.0.md) | Nov 1, 2021 |

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Data as of 2026-11-09T07:25:28Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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